1. Field of the Invention
This invention relates generally to assemblies and methods for separating fluids from particulate matter and particularly to the separation of plasma or serum from blood by filtration. This invention is particularly directed to filtration assemblies using glass fibers under direct pressure resulting in compression of the glass fibers to specified densities. The high or positive pressure on the filter or filter layers is applied and maintained throughout the filtering process.
2. Description of the Background
Compounds associated with diseases or health conditions such as metabolites or drugs are often found in body fluids such as blood. Therefore, in clinical laboratories, blood is used for diagnostic determinations or tests in order to provide information about the health status of patients. Blood is comprised mainly of corpuscular or particulate matter, for example, red and white blood cells and fluid matter such as serum or plasma. Generally, in clinical laboratories, when a test for a particular blood analyte is needed, the patient's blood which has been transported to the laboratory, is first separated from the serum (blood is allowed to clot with no anticoagulants present) or plasma (blood is drawn in the presence of anticoagulants) by centrifugation. Subsequently, the plasma or serum is used for the measurement of the particular analyte using automated instrumentation. This is a time-consuming process. However, when an urgent or emergency situation arises, tests or assays need to be performed which can yield results rapidly and at the patients' site. These urgent situations cannot be satisfactorily met with tests that need transportation, automated instrumentation or highly trained personnel. Therefore, the tests or devices which can be used for on-site testing with a rapid turnaround time require a blood separation method which will permit the separation of serum or plasma from blood in less than 15 seconds and preferably in 2-10 seconds, will completely remove red blood cells, and will not be technique dependent, such as wiping or washing of red blood cells.
A number of techniques have been devised to accomplish this difficult separation. All techniques utilize a filtering step capable of separating red blood cells. Numerous materials have been used in the past as filters utilizing certain conditions, composition, and devices. Papers, non-woven fabrics, sheet-like filter material composed of powders, or fibers such as man-made fibers or glass fibers and membrane filters having suitable pore sizes have been proposed. Although glass fibers have been known in the prior art as a material used for this separation process, subsequent improvements utilizing several specific methods have been claimed to give different degrees of speed and/or completion of separation. For example, Moyer et al. uses glass fibers for filtration of blood as described in U.S. Pat. No. 3,791,933. U.S. Pat. No. 4,256,693 to Kondo et al. discloses a number of filter materials, including glass fibers, in a multi-layered integral chemical analysis element for use in blood separation. Subsequently, Vogel et al., U.S. Pat. No. 4,477,575, showed a composition and process for allowing the separation of serum from whole blood consisting of glass fibers having an average diameter of 0.2.mu. to 5.mu. and a density of 0.1 gm/cm.sup.3 to 0.5 gm/cm.sup.3 without applying any positive pressure and which generally takes 1 to 5 minutes for separation of plasma from blood. Subsequently, Hillman et al., in U.S. Pat. No. 4,477,575, showed a blood separation device using glass fibers to separate plasma from blood where the filtration is carried out at low pressures. The filter in this latter invention only retards the flow of red blood cells. However, these prior art techniques are not suitable where faster flow rates, for example, in less than 15 seconds and preferably in 2-10 seconds, are desired as well as the complete retention of the cells, i.e., determination of analytes needed for urgent care drug overdose cases, such as acetaminophen, theophylline, digoxin, salicylate, etc.
Despite the need for assemblies and methods to quickly separate plasma or serum from whole blood, and which overcome the limitations and problems of the prior art, none insofar as is known has been proposed or developed.
Accordingly, it is an object of the present invention to provide assemblies and methods to further refine and advance blood separation techniques.